You're on the right path, but you have forgotten to add in the charges-per-day calculation.
Let's try this again: (spell level) * (caster level) * 1,800gp, divided by (5 divided by charges per day)
So 2*3*1800/(5/14400) = 31,104,000gp. You are aware that there are 14,400 standard actions in a...